The present invention relates to a so-called engagement profile or a beam.
A beam according to the present invention is preferably made of thin steel plate by bending in such a way that the beam comprises one or several web plates extending lengthwise of the beam substantially at a constant distance from each other and perpendicular or inclined relative to the fastening plane of the beam. These web members are interconnected by members of the same sheet material. Thus, the beam is preferably made of a single sheet blank. For fastening it to its underlaying bed, the beam further comprises one or several fastening strips, which are preferably integral parts of the web members and whereby the beam is fastened to a board supported by said beam. Such a supported board can be made of wood, such as boards, woodboard, plywood, blockboard, chipboard, fiberboard, gypsum board or the like, into which the engagement profiles formed in a known manner on fastening strips sink and engage as the strips are clamped against the board e.g. by means of a suitable press. The beam can also be used for supporting and reinforcing a concrete slab, whereby it is placed on top of a concrete slab during its casting prior to the setting of concrete, with the studs engaging in concrete. Thus, in a particularly preferred case, the studs are designed so that the blade side of studs is provided with a transverse toothing or roughening, as disclosed in the Applicants' earlier Finnish Pat. No. 65643.
A drawback with the above type of beam is, however, a relatively weak strength under major stresses as the sheet material of such beam is thin, the sheet thicknesses being e.g. 1-1.5 mm. Such a thin sheet material begins to fracture quite easily because of buckling. In order to provide a beam with greater strength, it can of course be made of a thicker sheet material. However, manufacturing will be more difficult and costs will be higher because the raw material is more expensive and working is more difficult. Especially, the preparation of engagement studs will be more difficult with thicker sheet material.
When studying tensions in the above type of beam it can be noted, especially as far as bending is concerned, that the greatest stresses occur in the upper and lower portions of the beam cross-section while in the midportion, in a so-called neutral plane, the stress is zero. In the upper edge of the cross-section, for example in fastening strips, there prevails a compression stress while in the lower edge there is accordingly a tensile stress. Some of the stress in the fastening strips is naturally taken up by the plate or board which is supported by the beam, but if this plate is weak, the stress on the strips may become too great, especially since such strips are weakened by the reduction in the amount of basic material as a result of stamping of the studs.
The object of the invention is thus to provide a solution to the above problems and to improve the strength of an engagement beam without substantially increasing the actual material thickness of a beam so as not to unduly increase the weight and manufacturing costs of a beam.
The invention will now be described in more detail with reference made to the accompanying drawings which illustrate a few preferred embodiments of the invention and their details and advantages. In the drawings